package seqlist.oj;

public class Num21 {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1==null ){
           return l2;
        }
        if(l2==null){
            return l1;
        }
        ListNode dummyHead=new ListNode(-1);
        ListNode last=dummyHead;
        while(l1!=null && l2!=null){
            if(l1.val<=l2.val){
                last.next=l1;
                last=l1;
                l1=l1.next;
            }else{
                last.next=l2;
                last=l2;
                l2=l2.next;
            }
            if(l1==null){
                last.next=l2;
            }
            if(l2==null){
                last.next=l1;
            }
        }
        return dummyHead.next;

    }
}
